Analysis of liquid samples typically involves aspiration of liquid from the sample through a conduit having a metered aperture at its immersed end. The typical particle analyzer consists of three components: a sample vessel, a liquid flow system, and a sensor.
Particle analyzers move suspended biological or industrial particles from the sample vessel to the sensor, via the liquid system. The sensor detects, counts, and identifies the particles. The liquid flow system then moves the sample into a waste container.
Detecting, counting and identifying particles can be done by a variety of sensors. These include impedance, light scatter, and fluorescence type sensors. Regardless of which sensing mechanism is used, the analyzer also needs a liquid flow system.
Many instruments need prepared samples for analysis. The preparation may be as simple as mixing the sample with a reagent. Usually, sample preparation is a two step process. First, the sample is collected in a suitable vessel and then it is prepared by diluting it in salt water. After the analytical cycle is complete, a valve must be closed to prevent draining of the diluent supply from the system by siphon action before new liquid samples are situated for analysis. Conventional liquid flow systems use a combination of pinch valves and/or stopcocks to accomplish this task. These methods are deficient because stopcocks must be manually operated, while normally-closed pinch valves have a tendency to cause a permanent deformation of the system tubing. In addition, most liquid systems for analytical instruments use stepper motors or peristaltic pumps, timing controls, and diluting assemblies. These precision liquid systems are expensive, complex, and require periodic maintenance for reliable operation. This is especially true of systems used to analyze microscopic particles such as red and white blood cells.
In addition, the current design of most particle collection and dilution assemblies have deficiencies in their design and operation which reduce the accuracy and efficiency of their measurements and the complexity of maintenance. Collectively, these features decrease the efficiency and drastically increase the cost of operation of such analytical instruments. There exists, therefore, a need for a simple yet reliable liquid control system which overcomes these deficiencies by eliminating the pinch valves and manually operated stopcocks yet provides for reliable, low maintenance operation.
It is an object of the present invention to provide a self-filling, anti-siphon liquid flow system devoid of pinch valves or manually operated stopcocks and which is simple to operate and maintain.
It is an additional object of this invention to provide an analytical instrument for detecting, counting and identifying particles which has multiple liquid flow sub-systems to aspirate samples from multiple sample containers and which may have multiple analytical channels.